Fred Greanoff of Lancaster has written to ask a question about feeder birds that has been posed to me several times this winter and last.
"Having had a bird feeder in my yard for many years," he wrote, "I have noticed the decline in the presence of the house finch and purple finch. At one point they were about the only bird present, as they liked the black oil seed that I put out. The decline has been over a period of two years to the point now that I never see a one. The sparrows have taken over completely, with an occasional blue jay and cardinal.
"Is this a migration thing, territory takeover by the sparrows or just one of those things?"
Before responding to this inquiry, I note that it is easy to confuse house and purple finches, for they look much alike. Male purple finches are best described as sparrows dipped head-first in cranberry juice: Their heads, breasts and backs are largely purple. Female purple finches do not show this color and are simply streaked with brown, but the distinctive white streak above their eye separates them from the similarly colored female house finches. The color of male house finches varies from red to orange and even to yellow but is never purple, and their color does not extend to their backs. The purple finch is by far the less common, except in a few Southern Tier locations.
House finches are not native to this region. Their range was originally Western, and until 1940 they were often illegally captured there and sold in the East as cage birds called Hollywood finches.
When this trade was discovered by Fish and Wildlife Service agents, the New York City dealers simply released the birds. Remarkably, they established a Long Island colony and did so well there that they began to extend their new range. I lived in Connecticut in the early 1960s, and they appeared at our feeders then. They reached the Niagara Frontier by the mid-1970s, and a few years ago the Eastern and Western populations met to cover the country.
These newcomers had a noticeable effect on local populations of house sparrows. Except on farms, the more aggressive house finches displaced the sparrows, and the house sparrow population plummeted.
But Greanoff's observation is on the mark. Suddenly a few years ago, the house finch population began to decline. The cause: a strain of avian conjunctivitis. It spread rapidly among these birds, causing their eyes to become swollen and crusty. This often leads to blindness and death from starvation, as the birds cannot forage for food. (A more benign form of human conjunctivitis is called pink eye.)
The avian disease is communicated when healthy birds come into contact with an infected bird -- as in a crowded roost -- or with an object touched by one of them, like those tube feeders on which the bird must stick its head into a hole in order to extract seeds. When the eyes of an infected bird come in contact with the opening, the next bird to feed at that perch may pick up the disease. For this reason, all feeders should be cleaned with a solution of one part bleach to 10 parts water every two weeks or so.
The disease infects poultry and has been detected in a few goldfinches as well. But it is not transferable to humans.
As Greanoff further observes, the house finch decline is indeed counteracted by a house sparrow increase.